The present invention relates to a cell exchanging device, more particularly to an Asynchronous Transfer Mode ( ATM) relay exchanging device which exchanges an ATM cell cellularized by an ATM Adaptation Layer (AAL) type 2.
The ATM adaptation layer (AAL) enhances the service provided by the ATM layer to support functions required by the next higher layer. The AAL performs functions required by the user, control and management planes and supports the mapping between the ATM layer and next higher layer. The functions performed in the AAL depend upon the higher layer requirements. In an International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), four types including an AAL type 1 (AAL1), an AAL type 2 (AAL2), an AAL type 3/4 (AAL3/4) and an AAL type 5 (AAL5) are defined as an AAL protocol in the ITU-T recommendations I.362 and I.363. The AAL1 is mainly used when voices of 64 kbit/s are transferred on the ATM. The AAL2 is used when low bit rate voices compressed and encoded to 8 kbit/s or the like are transferred on the ATM. The AAL3/4 and the AAL5 are mainly used when data is transferred on the ATM.
FIG. 22 shows an explanatory view of an AAL2 cellularizing system. In order to transfer a low bit rate voice with little delay and high efficiency, as shown in FIG. 22, the AAL2 (ITU-T recommendation I.363.2) presents a 3-octets Common Part Sublayer (CPS) packet header, which includes an identifier called Channel Identifier (CID), to each of voice channels (CPS-packetting), and multiplexes and packs a plurality of CPS packets in a single ATM cell. Accordingly, a plurality of AAL2 level connections are multiplexed in a single Virtual Channel (VC) connection of the ATM.
As shown in FIG. 22, the CPS packet is composed of a 3-Bytes packet header and a variable length CPS packet payload portion, and besides the foregoing CID the CPS packet header is composed of a Length Indicator (UL) for storing the packet length of the CPS packet and an User-to-User Indication (UUI) that is a user-to-user identifier and a Header Error Control (HEC) for controlling a header error.
When an application of AAL2 to a network is considered, with regard to the AAL2, CPS packets having a different CID are multiplexed and packed into a single ATM cell, so that VC connections between nodes must be provided in a mesh form when a network is constructed by only an existing VC switch. For this reason, there has been a problem that the number of VC connections significantly increases as the number of nodes increases. As means for solving this problem, as an example shown in, for example, xe2x80x9ca study on a method for constituting a network using an AAL type 2xe2x80x9d of TR of IEICE SSE98-119, 1998, a method in which AAL2 level connections connected to different nodes are multiplexed and packed into one VC connection and an AAL2 level switching is performed in an intermediate node has been known to be effective. As described above, by providing an AAL2 level switching function in the network, it is satisfactory that the VC connection is set only for an adjacent node, thus preventing an increase in the number of the VC connections.
Next, in FIG. 23 an explanatory view of conversion example from an AAL2 cell to an AAL2 partial fill cell is shown. As described above, in the AAL2 the CPS packets having different CIDs are multiplexed and packed into one ATM cell. For this reason, in order to carry out the AAL2 level switching, a switching for each of the CPS packets is necessary, so that an existing ATM switch cannot be used as it is. Accordingly, in order to perform the AAL2 level switching using an existing ATM switching, as shown in FIG. 23, in an ATM line corresponding section, it is required to convert the ATM cell (hereinafter referred to as an AAL2 cell), in which a plurality of CPS packets are multiplexed and packed, to an ATM cell (hereinafter, referred to as an AAL2 partial fill cell), which is constituted by only one CPS packet, before entering into the ATM switch.
When the ALL2 cell is converted to the AAL2 partial fill cell in the ATM line corresponding section before the entry into the ATM switch, as shown in FIG. 23, the number of the ATM cells increases compared to that before the conversion an the example shown in FIG. 23, since one ATM cell is converted to the four AAL2 partial fill cells, a throughput is quadrupled.) Moreover, since the CPS packet takes a variable length form, the number of the ATM cells after the conversion varies. Accordingly, when the AAL2 level switching is carried out by the existing ATM switch, a new problem arises, in which the AAL2 partial fill cells have an effect on a transfer of the ATM cell cellularized by an AAL other than the AAL2. To be specific, since the AAL2 cell was converted to the AAL2 partial fill cells, the throughput after the conversion increases, and such a case in which an output of the ATM cell cellularized by other AALs is delayed or the ATM cell is discarded by the AAL2 partial fill cells may arise.
Considering the foregoing points, the object of the present invention is to avoid an influence which the AAL2 partial fill cells have on a transfer of the ATM cell cellularized by an AAL other than the AAL2, by assigning a priority order in which each of cells are transferred, under the condition where the AAL2 partial fill cells and the ATM cell cellularized by an AAL other than the AAL2 are mixed.
Furthermore, in order to use the AAL2 partial fill cells with an existing ATM switch, the object of the present invention is to achieve an AAL2 level switching using an existing ATM switch by providing information for identifying the AAL2 partial fill cells in an ATM cell header within a device.
When the AAL2 cell is converted to the AAL2 partial fill cells in the ATM line corresponding section, the object of the present invention is to prevent the effect on the AAL2 partial fill cells and deterioration of a transfer quality of ATM cells in spite of an increase in the number of the ATM cells after the conversion, by performing a priority control in an ATM cell level depending on a grade of quality.
In the present invention, provided are an ATM cell demultiplexing section for extracting and separating only AAL2 cell from each of ATM cells in an ATM line corresponding section on an input side; a cell conversion section AAL2 DMX for converting the AAL2 cell to AAL2 partial fill cells; and an ATM cell multiplexing section for multiplexing ATM cells other than the AAL2 partial fill cells and the AAL2, and a priority order for each of the ATM cells is determined based on class information presented in the ATM line corresponding section, before the ATM cells are inputted to an ATM switch section, and reading-out from the ATM cell multiplexing/packing is controlled. Similarly, in an ATM line corresponding-section on an output side, provided are an ATM cell demultiplexing section for extracting and separating only AAL2 partial fill cell from each of ATM cells; a cell conversion section AAL2 MUX for converting from the AAL2 partial fill cells to the AAL2 cell; and an ATM cell multiplexing section for multiplexing the ATM cells other than the AAL2 cell and the AAL2, and when the ATM cell is transferred on a transmission path, a priority order for each of the ATM cells is determined based on class information presented in the ATM line corresponding section on the input side and reading-out from the ATM cell multiplexing section is controlled, whereby an AAL2 level switching can be realized using an existing ATM switch.
According to the means for solving the subject of the present invention, provided is a cell exchanging device which exchanges a plurality of variable length packets multiplexed and packed into one cell to be transferred in an Asynchronous Transfer Mode, comprising:
a plurality of receiving interface sections for receiving a cell;
a plurality of transmitting interface sections for transmitting the cell; and
a switching section for exchanging the cell to which the foregoing receiving interface sections and the foregoing transmitting interface sections are connected, wherein:
each of the foregoing receiving interface section includes a receiving cell transfer control section which disassembles the received cell to demultiplex and unpacked the plurality of variable length packets multiplexed and unpacked in the received cell, and converts the received cell to a cell which has one of the demultiplexd and unpacked variable length packets, thereby transferring the cell to the foregoing switching section,
the foregoing switching section transfers the cell transferred from the foregoing receiving interface section to the foregoing transmitting interface section where a transmsssion processing is performed depending on a header value of the cell, and
the foregoing transmitting interface section includes a transmitting cell transfer control section which demultiplexs and unpacks the variable length packet from the cell transferred from the foregoing switching section and multiplexes and packs a plurality of variable length packets in one cell, the plurality of variable length packets corresponding to the same output path.